A rotary hammer, such as a hammer drill, is designed to impart axial percussive vibrations along with rotation to a tool, such as a drill bit, held at the front end of the hammer body, so as to perform chipping and drilling operations. The construction of such rotary hammer is disclosed, e.g., in U.S. Pat. No. 4,280,359, wherein a reciprocable piston-like drive member is installed in a cylinder which guides a vibrating mechanism disposed inside the hammer body, said drive member being adapted to be driven by an electric motor through a motion conversion transmission mechanism which converts rotary motion into axial reciprocating motion, the reciprocating motion of said drive member imparting axial percussive vibrations to a tool, such as a drill bit, held at the front end of the hammer body through a striker axially movably installed in the cylinder, and concurrently with this impartation, the rotation of the electric motor is reduced and imparted to a tool holding member which concomitantly rotatably holds the tool, whereby percussive vibrations and rotation are imparted to the tool.
In the conventional rotary hammer as described above, the cylinder provided with the piston-like drive member and striker, and the motion conversion transmission mechanism and electric motor which form a drive section for driving said piston-like drive member are received by a frame forming a shell barrel, while a bracket section for rotatably supporting the tool holding member at the front end of the hammer body and a bracket section for holding a bearing which supports one end of the rotor of the electric motor are integrally formed and fixed on said frame.
As a result, in assembling this rotary hammer, the tool holding member and electric motor must be built into the bracket which supports them before said bracket can be fixed to the frame and, moreover, after the electric motor and tool holding member have thus been built in, the bracket which holds the cylinder with the piston-like drive member and the motion conversion transmission device is fixed to the frame, a fact which, coupled with the substantial complexity of the internal construction, makes the assembly operation very troublesome. Further, disassembly operation which becomes necessary, e.g., when a machine trouble occurs is never easy as it must be performed in the order reverse to that for assembly operation. Particularly, the rugged the shell of the hammer body is made so as to have sufficient shock resistance to endure a long period of use, the more difficult the assembly operation.
In this type of rotary hammers, which requires operation performance tests, e.g., on the electric motor during assembly operation, if the hammer body is of unitary construction as described above, an operation performance test, e.g., on the electric motor must be conducted with not only the electric motor but also the bit or other tool holding section built into the shell barrel; thus, such test is very troublesome.
Further, in this type of rotary hammers, it often occurs that the internal mechanism breaks down or that the hammer fails to operate owing to the consumption of parts such as the sealing rings for the piston-like drive member. With the hammer body construction difficult of disassembly as described above, repair of damage or replacement of parts cannot be easily made in the field and the difficulty of disassembly often makes it necessary to carry the rotary hammer to the factory, during which time another rotary hammer has to be used.
For this reason, in another example of prior art, the shell serving as a frame for holding various parts is bisected along the axis of the vibrating mechanism to make it possible to open the shell to opposite sides. With this arrangement, although the assembly operation is easy, in disassembly all the parts are exposed and unnecessary parts are also disassembled. Moreover, since the split type shell halves on opposite sides must be clamped together as by screws, a number of fastening parts such as screws are required and the construction must be such that the fastening parts will not become loose under heavy shocks, a fact which makes disassembly operation more difficult. Further, the aforesaid split construction renders the parts liable to loosen, lowers the accuracy of assembly and fails to provide sufficient reliability in shock resistance; therefore, it is not preferable in practice.
Thus, it is less easy than expected to provide a rotary hammer which is easy to assemble and disassemble and which has high quality and high reliability. The fact is that rotary hammers are manufactured with it being admitted unavoidable that repair and replacement of parts take much time and labor.
Accordingly, I proposed a rotary hammer to solve the aforesaid problems (Japanese Patent Application No. 108602/1984). The present invention is an improved version of the same.